Elevated levels of tyrosine kinase activity are necessary the growth and dissemination of malignant carcinoma cells. Our laboratory recently applied new technologies in monoclonal antibody production and identified dramatic changes in the expression and function of the EphA2 tyrosine kinase in malignant carcinomas. EphA2 is overexpressed in cancer cells (by 50-500 fold), with the highest levels of EphA2 consistently found on cells with metastatic potential. We have also shown that EphA2 overexpression confers metastatic potential but that the growth and invasiveness of metastatic cells can be reversed by activating EphA2 at the cell surface. Based on these results, we hypothesize that EphA2 provides unextraordinary opportunity for antibody-based targeting of metastatic carcinoma. To test this, we recently used innovative strategies to generate antibodies against epitopes on the extracellular domain of EphA2. Here, we propose to develop new assay systems to test EphA2 as a target for monoclonal antibody treatment of metastatic cancer cells. Our Specific Aims are: i) to identify EphA2 antibodies that can target tumor cells, ii) to test if these antibodies block metastatic cell growth or invasiveness, and iii) to determine the mechanisms of antibody action. Upon conclusion of our studies, we will have validated EphA2 as a molecular target for cancer treatment and will have generated the reagents and expertise to exploit a critical vulnerability on malignant cells.